Introduction

In the year 2002 an 8 MW CHP plant
based on a circulating fluidized bed steam blown gasifier
producing heat and power (4.5 MWth, 2 MWel) with a gas
engine went into operation in Guessing, Austria. At the
middle of 2002 the gasifier and the gas cleaning system
was coupled with the gas engine.
Renet-Austria, a competence network on energy from
biomass, consisting of experts from universities and
industry started to develop this process further to a
commercial stage. During the last years a lot of
improvements could be reached. These improvements
were connected on the one hand with changes in
construction (e.g. feeding system, online particle
separation) and on the other hand with advances in the
operation performance. The latter is described here.
Due to the excellent performance that was reached
during the last years, several additional research projects
could be started in Güssing. The producer gas from the
circulating allothermal fluidized bed gasifier is nearly
free of nitrogen and has an high hydrogen content.
For this reason it is well suited for fuel cells as well as
several synthesis products. Therefore, projects aiming at
the development of processes for the production of
synthetic natural gas and Fischer Tropsch liquids are
currently carried out. First results and further planning
are shown in the second part here.

Description of the Biomass CHP Güssing

In Guessing an innovative process for combined heat
and power production based on steam gasification has
been successfully demonstrated. Biomass is
gasified in a circulating dual fluidised bed reactor. The
producer gas is cooled, cleaned (2 stages) and used in a
gas engine. Wood chips from forestry are the main fuel for the
demonstration plant. The wood trunks are dried naturally
by storage of about 1-2 years in the forest. Then they are delivered to the CHP-plant and chipped there. When the
biomass is used, it has a water content of about 25-40%.
The heat produced in the process is partly used
internal, e.g. for air preheating, steam production, etc.,
and the rest is delivered to an existing district heating
system. The net electricity produced is delivered to the
electrical grid. The feed in rate in Austria is regulated by
law and depends on the type of biomass used and on the
size of the plant (13-16 Cents/kWh).

Characteristic design data of Biomass-CHP

design data

operating data

Start up of gasifier

November 2001

Start up of gas engine

April 2002

Fuel

wood chips

wood chips

Fuel water content

15%

25-40%

Fuel Power

8000 kW

8500-9500 kW

Electrical output

2000 kW

2000 kW

Thermal output

4500 kW

4500 kW

Electrical efficiency

25.0 %

20-23 %

Thermal efficiency

56.3 %

45-53 %

Total efficiency

81.3 %

65-76 %

Biomass chips are transported from a daily hopper to
a metering bin and fed into the fluidised bed reactor via
screw feeders. The fluidised bed gasifier consists of twozones, a gasification zone and a combustion zone. The
gasification zone is fluidised with steam which is
generated by waste heat of the process, to produce a
nitrogen free producer gas. The combustion zone is
fluidised with air and delivers the heat for the gasification
process via the circulating bed material.
A water cooled heat exchanger reduces the
temperature from 850°C – 900°C to about 150°C –
180°C.The producer gas is cooled and cleaned by a two
stage cleaning system. The first stage of the cleaning
system is a fabric filter to separate the particles and some
of the tar from the producer gas. These particles are
recycled to the combustion zone of the gasifier. In a
second stage the gas is liberated from tar by a scrubber.
Spent scrubber liquid saturated with tar and
condensate is vaporized and fed for thermal disposal into
the combustion zone of the gasifier. The scrubber is used
to reduce the temperature of the clean producer gas to
about 40 °C. The clean gas is finally fed into a gas engine
to produce electricity and heat. If the gas engine is not in
operation the whole amount of producer gas can be
burned in a backup boiler to produce heat.
The flue gas of the gas engine is catalytically
oxidised to reduce the CO emissions. The sensible heat of
the engine’s flue gas is used to produce district heat. The
flue gas from the combustion zone is used for preheating
air, superheating steam as well as to deliver heat to the
district heating grid. A gas filter separates the particles
before the flue gas of the combustion zone is released via
a stack to the environment.
The plant fulfils all emission requirements. The
operation experience shows that there is only one solid
residue which is the fly ash from the flue gas. This fly ash
fully burned out, the loss of ignition is lower than 0.5 w-
%. The plant produces no condensate which has to be
disposed externally.

Operation Performance of the Biomass CHP Güssing

Overall operation performance

The Güssing plant is in operation continuously since the
middle of the year 2002. Of course during this time there
were several periods of maintenance and also periods for
improvement of the construction. Heat is fed into an
existing district heating system and electricity into the
power grid. Fig. 2 shows the cumulative production of heat and
power since January 2002. The production of electricity
started in the middle of the year 2002. From the following figure it
can be seen clearly that there were only a few periods
were the plant was not in operation. Furthermore, also an
increase of the heat and power output can be observed.

Reduction of operation means

Since the beginning of operation of the demonstration
plant the improvement and optimisation of the operation
performance was a permanent task. This optimisation
work carried out by Renet-Austria leads to a reduced
amount of operation means and also a reduction of waste
material which means fly ash from the flue gas line.
The following figure shows the development of the main operation
means over the last years.

Nitrogen is used as purge gas at all entrances to or
exits from the plant. Furthermore, nitrogen is used also
for removing the dust from the fabric filter in the
producer gas line. From 2003 to 2005 the nitrogen
consumption could be reduced to about 50 % of the
original amount.
As gasifier a circulating fluidized bed technology is
applied. This means that a bed material is necessary
which has a certain attrition rate during operation. This
attrition rate and therefore the loss of the bed material
depends mainly on the kind of the material, the velocities
of the riser, and also the separation efficiency of the
cyclone. On the base of the operation experience, some
simulation work, and optimisation of these parameters a
reduction of the bed material loss by more than 70 %
could be obtained.
Another material necessary for the operation is the
so-called precoat material. This precoat material is
necessary to avoid condensation of tar compounds
directly on the filter bag which could lead to plugging or
even to damage of the filter cloth. At the beginning a
swing operation with two filters (one in operation mode,
on-line, another in pre-coating mode, off-line) are
applied. Now this operation mode has been change to an
online operation which works without any problems. This
leads to a dramatic reduction in the need of the precoat
material down to about 20 % of the original amount and
also to a reduction in the nitrogen consumption (see
obove).
The scrubber for the tar separation is operated with
biodiesel. The spent biodiesel together with some condensate is fed into the combustion chamber of the
gasifier. With this scrubber the overall tar in the producer
gas can be removed over 90 %. The operation experience
leads to a slight reduction of the biodiesel of about 25 %.
The general aim of all these efforts is the reduction of
the costs and therefore the improvement of the economy
of the plant.

One further cost effective operation means is the
engine oil. The experience of previous plants shows short
operation times of about 500 hours which means high
costs. With the aid of additives an essential increase of
operation times without change of the engine oil could be
obtained.
the following figure shows the increase of the total acid number
with time for four different engine oils (different
additives). If the limit of the total acid number (2.5 mg
KOH/g) is exceeded the oit has to be changed. The current status is that operation hours of about 4000
hours are possible with the same engine oil without any
serious problems.

Availability of the plant

It is clear that the availability of any demonstration
plant can not be as high as for a plant which uses an
already mature technology. For such an innovative
technology as it is used in the case of the CFB
allothermal steam gasification plant and the gas cleaning
system several years of operation experience are
necessary to remove all the weak points within the plant.
The following figure shows increase of the availability for the
gasifier and also for the gas engine for the years from
2002 until 2006. It can be seen that the availability could
be increased essentially over time and it reaches now
more than 90 % for the gasifier and more than 85 % for
the gas engine in the year 2006.

Research Projects

The favourable characteristics of the product gas (low
nitrogen content, high hydrogen content, H2:CO ratio of
1.6 – 1.8) allow also other applications of this producer
gas. Research projects concerning the production of
electricity in a SOFC (solid oxide fuel cell), the synthesis
of SNG (synthetic natural gas), and Fischer-Tropsch
liquids and have been started.
The following figure gives an overview about possible applications
of the producer gas from a steam blown gasifier.

In
principal, all products can be obtained from the synthesis
gas as this is the case for coal or crude oil. All the
necessary chemical pathways are well known since many
decades. Therefore, in analogy to coal or oil chemistry
one can say now “green chemistry” if the original
material is renewable (e.g. biomass). All this advanced applications need an ultra-clean
synthesis gas. To cover with these requirements further
cleaned up and conditioning steps are necessary. For this
purpose a slip stream of the synthesis gas is taken, treated
in a suitable way, and fed to the research installations.
The following figure shows a principle scheme of this arrangement.

Status till 2009

Status from 2009

In 2009 Renet Austria and the Austrian Bioenergy Centre merged together and formed BIOENERGY2020+, a centre of excellence, funded by the COMET programme from Austria. With the support of BIOENERGY2020+ a new Technikum was erected, where now R&D on FT, mixed alcohols or hydrogen is done.